The gunman behind the Connecticut elementary school massacre stormed into the building and shot 20 children at least twice with a high-powered rifle, executing some at close range and killing adults who tried to stop the carnage, authorities said Saturday.

Twelve girls and eight boys. One had celebrated her seventh birthday just four days before her death.

Dressed in "cute kid stuff," all 20 died when a heavily armed 20-year-old gunman forced his way into their school, Sandy Hook Elementary, and shot them and six women in an act of violence that has shattered their once-tranquil suburban town.

"They were first-graders," said Connecticut Chief Medical Examiner Dr. H. Wayne Carver II, before releasing the names of all the victims of the school shootings on Saturday. The children were all six and seven years old. It has been confirmed that the youngest victim was Jewish six-year-old Noah Pozner.

Asked to describe the attack, Carver, who oversaw the autopsies of all the victims and conducted many himself, called it "the worst I have seen."

The shooter, identified by law enforcement officials as Adam Lanza, killed his mother Nancy on Friday, then drove to the school where he gunned down another 26 people before taking his own life in one of the deadliest mass shootings in U.S. history.

He fired a rifle, shooting his victims multiple times .Parents identified their children through pictures, a process intended to minimize their shock, Carver said.

Police did not officially identify Lanza or his mother, but his father on Saturday issued a statement saying he too was struggling to understand his son's actions.

"No words can truly express how heartbroken we are," Peter Lanza said. "We are in a state of disbelief and trying to find whatever answers we can."

Members of the close-knit community went into public mourning on Saturday as the depth of the tragedy became clear.

" I don't know how to get through something like this," said Robbie Parker, a 30-year-old physician's assistant whose 6-year-old daughter Emilie was among the dead.

"My wife and I don't understand how to process this and how to get our lives going," Parker told reporters. The oldest of his three kids, Emilie, "could just light up a room," he said.

While Americans have seen many mass shootings in the past decades, the victims have rarely been so young. On Saturday, some Democratic lawmakers called for sweeping new gun-control measures, a move certain to run up against stiff opposition from the nation's powerful pro-gun lobby.

President Barack Obama plans to travel to the affluent suburb of 27,000 people about 80 miles from New York City on Sunday to meet with victims' families and speak at a vigil at 7 P.M. local time, the White House said in a statement.

Christmas tree memorial

Townsfolk packed into the church memorial services held throughout the day. On Saturday night, the pews at St. Rose of Lima were packed with parishioners standing at the rear of the church.

At least one person was missing - 6-year-old Olivia Engel, who was to have had a role in the Nativity concert.

"She was supposed to be an angel in the play," said Revered Robert Weiss. "Now she's an angel up in heaven."

Town fire officials set up 26 Christmas trees, decorated with stuffed animals, near the school as a memorial to the victims - many of whom were children who may have been hoping for such toys as their own holiday presents. Churches held memorial services.

"Those innocent little boys and girls were taken from their families far too soon," said Connecticut Governor Dannel Malloy.

"Let us all hope and pray those children are now in a place where that innocence will always be protected."

One of the victims, Josephine Gay, had celebrated her seventh birthday on Tuesday.

Rabbi Shaul Praver said he had spent time with Veronika Pozner, whose 6-year-old son Noah, was among the victims.

"She said that she didn't know how she was going to go on, and we encouraged her to focus on her other four children that need her and not to try to plan out the rest of her life, just take a deep breath right now," Praver said.

The adult victims, some of whom died defending the students, ranged in age from 27 to 56. Carver, the medical examiner, said all the bodies had examined had been shot with a rifle. He said he and his staff had not yet examined the shooter or his mother.

Motives emerging

Police earlier said they had assembled "some very good evidence" on the killer's motives.

"Our investigators at the crime scene … did produce some very good evidence in this investigation that our investigators will be able to use in, hopefully, painting the complete picture as to how - and more importantly why - this occurred," Connecticut State Police Lieutenant Paul Vance told reporters.

Yale-New Haven Hospital opened a crisis-intervention center in the wealthy suburb of 27,000 people about 80 miles from New York City.

The killer's mother, Nancy Lanza, legally owned a Sig Sauer and a Glock, both handguns commonly used by police, and a military-style Bushmaster .223 M4 carbine, according to law enforcement officials, who also said they believed Adam Lanza used at least some of those weapons.

The death toll exceeded that of one of the most notorious U.S. school shootings, the 1999 rampage at Columbine High School in Littleton, Colorado, where two teenagers killed 13 students and staff before fatally shooting themselves.

Around the nation communities took small steps to mark the tragedy.

At Virginia Tech, a Blacksburg, Virginia university where in 2007 a gunman killed 32 people in the deadliest school shooting in U.S. history, an announcer extended sympathies to the residents of Newtown before a basketball game.

"This campus ... shares a deep sense of grief," the announcer said. "We share that pain and we open our hearts to that community.